Re: Size Isn't Everything (WAS Re: cause of Gigantism in sauropods)

["Habib, Michael" <MHabib@Chatham.edu>]

This is an excellent point.  Prey preference would have been limited by size, 
but also by weaponry - so even similar sized theropods may have preferred 
different prey.  Size matters a lot, but so does the dental equipment.

--MH


On Feb 7, 2011, at 9:24 PM, Dan Chure wrote:

> The big, well known Morrison theropods (Allosaurus, Ceratosaurus, and 
> Torvosaurus) have strikingly different teeth.  Allosaurus has relatively 
> small, standard fare theropod teeth.  Ceratosaurus has long and very 
> blade-like tooth crowns.  Torvosaurus has large teeth with crowns that 
> remarkably robust.  The Torvosaurus teeth from Dry Mesa Quarry described 
> by Brooks Britt are way too large to fit in the mandible of the largest 
> Allosaurus (the roots would stick out of the ventral surface of the 
> dentary). Saurophaganax has one incomplete crown referred to it and that 
> seems to resemble Allosaurus as best one can tell.  Nothing is known of 
> the teeth of Epanterias.
> 
> It has long been recognized that Morrison sauropods have spoon shaped 
> teeth running the length of the jaws (Camarasaurids) and pencil like 
> teeth restricted to the front part of the jaws (diplodocoids).  This has 
> generally been regarded as reflecting some partitioning of the food 
> sources.  Might not the same be true of Morrison theropods and that the 
> widely differing tooth structure reflects either different prey or 
> hunting strategies?  The Morrison fauna is unusual (say compared to many 
> Cretaceous faunas) in that there are multiple, co-existing, large 
> theropods, with multiple genera co-occurring in the same quarries.
> 
> So guys, don't get hung up on size --- it isn't everything.
> 
> Dan
> 
> 
> 
> On 2/7/2011 6:11 PM, Habib, Michael wrote:
>> On Feb 7, 2011, at 7:29 PM,<vultur-10@neo.tamu.edu>  wrote:
>> 
>>> Yes, elephant-lion is rare.
>>> 
>>> But Cape buffalo are a *major* part of lion diet, IIRC more than half of 
>>> some lion populations' diet (Lake Manyara National Park is one, I think<60% 
>>> Cape buffalo) and that's something like 3-4x the lion's mass; especially 
>>> since lionesses do most of the hunting, and they're often like 120kg 
>>> animals, not 200kg. *Allosaurus amplexus* or *Saurophaganax* were larger in 
>>> comparison to *Diplodocus carnegii*.
>> Group attacks by lion on cape buffalo are common in some populations, true, 
>> but I am under the impression (admittedly from older literature) that solo 
>> attacks on such animals is extremely rare.  Taking into account that the 
>> average hunting group of lions is at least 3-4 individuals strong, that 
>> means that the mass ratio is actually close to 1:1, with the added 
>> advantages that a group of attackers naturally has on a single target.
>> 
>> 
>>> And what were *Allosaurus amplexus* and *Saurophaganax* --doing-- if they 
>>> weren't specialist sauropod, possibly big-sauropod, killers? Everything 
>>> else *A. fragilis* was quite big enough to deal with.
>> I suggest that perhaps they were killing larger juveniles, primarily.  Under 
>> that model animals such as A. fragilis would be killing smaller juveniles 
>> and the adults of small ornithopods, etc.  There's no reason to expect that 
>> any animals must have regularly predated the adults of large sauropods.  And 
>> there is no reason that the prey sizes could not overlap significantly; prey 
>> sizes taken by large carnivorans in semi-arid African habitats overlap quite 
>> a bit among multiple predators.  Far more is made of niche-partitioning that 
>> probably aught to be.
>> 
>> 
>>> But yes, the real titans were probably safe most of the time barring really 
>>> hungry / desperate theropods. Still, the idea you sometimes see that 'adult 
>>> sauropods were basically immune to predation' needs, at the least, 
>>> qualification.
>> True enough.  However, the reverse notion, that theropods regularly mauled 
>> giant sauropods to death, is seen very regularly, and seems highly 
>> implausible.  Adult sauropods were probably not immune to predation, but 
>> some of them were likely close.
>> 
>> Cheers,
>> 
>> --Mike
>> 
>> 
>> 
>>> William Miller
>>> 
>>> ----- Original Message -----
>>> From: "Michael Habib"<MHabib@Chatham.edu>
>>> To: vultur-10@neo.tamu.edu
>>> Cc: "dinosaur"<dinosaur@usc.edu>
>>> Sent: Monday, February 7, 2011 12:11:46 PM GMT -06:00 US/Canada Central
>>> Subject: Re: cause of Gigantism in sauropods
>>> 
>>> 
>>> On Feb 7, 2011, at 12:45 AM,<vultur-10@neo.tamu.edu>  wrote:
>>> 
>>>> So in the Morrison, the sauropod-theropod size gap seems smaller than the 
>>>> elephant-lion one. I see little reason to believe that Saurophaganax or A. 
>>>> maximus could not take down even Giraffatitan or Supersaurus.
>>> Neat comparison with the body mass estimates (thanks for punching the 
>>> numbers!) but I'm not sure I quite agree with your conclusion.  It seems 
>>> reasonable that something like Saurophaganax could take down something like 
>>> Giraffatitan under very rare, extreme circumstances, just as living 
>>> terrestrial macro-predators (or groups of them) very rarely kill much 
>>> larger animals than themselves.  However, I see no reason to expect that 
>>> such events were common, or even occurred with a high enough frequency for 
>>> us to seriously consider them as major factors in our  reconstructions of 
>>> Mesozoic ecology.  Living terrestrial vertebrate predators rarely take prey 
>>> even three times their own mass, much less 6-8 times.
>>> 
>>> The elephant-lion size ratio probably does not represent the ratio at which 
>>> predation is regular or ecologically important; at best it is a ratio at 
>>> which a very rare predation event is still barely feasible - and that is 
>>> for a specific guild of predators and herbivorous mammals.  The more 
>>> important size ratio is the maximum predator:prey mass ratio among 
>>> *regular* predation events.  Phrased as a question: Of those large 
>>> terrestrial animals that are predated as adults with a high enough 
>>> frequency for its impact on total population mortality to be measurable, 
>>> how large are their smallest predators (or total mass of packs, if they are 
>>> predated by groups)?
>>> 
>>> I don't know exactly what the answer to that question is, but qualitative 
>>> observation suggests that the size gap is pretty small.  The vast majority 
>>> of predators, even large ones, mostly take prey smaller than themselves.  
>>> Even animals like water buffalo, which are a fraction of the size of 
>>> elephants, are large enough as adults to be predated upon rarely (albeit 
>>> more often than elephants).
>>> 
>>> Cheers,
>>> 
>>> --Mike
>>> 
>>> 
>>> Michael Habib
>>> Assistant Professor of Biology
>>> Chatham University
>>> Woodland Road, Pittsburgh PA  15232
>>> Buhl Hall, Room 226A
>>> mhabib@chatham.edu
>>> (443) 280-0181
>>> 
>> Michael Habib
>> Assistant Professor of Biology
>> Chatham University
>> Woodland Road, Pittsburgh PA  15232
>> Buhl Hall, Room 226A
>> mhabib@chatham.edu
>> (443) 280-0181
>> 
>> 
>> 
> 
> 

Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181